This invention relates to pressure transducers.
One known type of pressure transducer is described in U.K. patent specification No. 827,344, and comprises a hollow resonantly vibratable cylinder closed at one end by an end cap, means for exciting and maintaining resonant vibrations of the cylinder and means for suppling a fluid whose pressure is to be sensed to either the internal or the external surface of the cylinder. This known type of transducer can be made to be extremely accurate, but in order to achieve such accuracy, it is necessary to use a relatively expensive material, with a low temperature coefficient of elasticity, for the cylinder, and it is also necessary to take great care in the manufacture of the cylinder. Further, even the currently most accurate versions of this type of transducer are still subject to a number of limitations: thus they are density sensitive as well as pressure sensitive, which can lead to an error of the order of 0.01% per .degree.C. as the density of the fluid changes with temperature; their cylinder material has a residual temperature coefficient of elasticity of the order of 10 p.p.m. per .degree.C.; they can be subject to long term drift of about 0.02% of full scale over six months; they are subject to an acceleration effect of up to 0.002%/g due to the cylinder end cap applying an axial force to the cylinder wall under axial acceleration; and because of the need to temperature conpensate for the aforementioned density sensitivity, it is difficult to make an accurate differential pressure version unless an absolute value of one of the pressures is known for compensation purposes.
It is an object of the present invention to provide a pressure transducer in which the effects of at least some of the abovementioned limitations are alleviated.